Gypsum amendment of agricultural fields to decrease phosphorus losses – Evidence on a catchment scale
2024
Ekholm, Petri | Ollikainen, Markku | Punttila, Eliisa | Ala-Harja, Venla | Riihimäki, Juha | Kiirikki, Mikko | Taskinen, Antti | Begum, Khaleda | Suomen ympäristökeskus | The Finnish Environment Institute | 0000-0003-3070-4570 | 0000-0002-9930-5706
Highlights • 14.9 km2 of fields were amended with gypsum and the riverine material fluxes were monitored before and after the treatment. • The fluxes of PP, TSS, and DOC decreased by 15%, 25%, and 8.9%, respectively, as a 5-year average. • Role of gypsum in the reduction could not be conclusively quantified due to differences in the erodibility between control and gypsum areas. Abstract Amending agricultural fields with gypsum has been proposed as a cost-effective measure to reduce P load on coastal waters. We treated 1490 ha of clayey fields with phosphogypsum (4 t ha−1) in Southwest Finland and monitored the recipient river with online sensors and water sampling for the preceding spring and 5 years after the amendment. Gypsum immediately decreased the riverine fluxes, the effect lasting at least 5 years for particulate P (PP), total suspended solids (TSS), and dissolved organic C (DOC) and 1–2 years for dissolved reactive P (DRP). Compared with an upstream control area, the fluxes of PP, TSS, and DOC decreased by 15%, 25%, and 8.9%, respectively, as a 5-year average. Assuming the change in the fluxes occurred only due to gypsum, the amended fields showed 35%, 59%, and 64% lower losses for PP, TSS, and DOC than the unamended ones. More than half of the gypsum remained in the soil even after 5 years; thus, although the efficiency of gypsum lessened over time, its residual effect may be present. However, the difference in the erodibility between the control and treatment areas impacted the validity of the results, especially as the pre-gypsum period was short. In addition, the performance of gypsum showed spatial variation.
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